摘要:

The paper deals with the equipment and construction of modern high-power testing laboratory capable of testing circuit breakers of ratings up to 1 500 MVA at voltages up to 132 kV.General details of the power circuit are given, including the generator, super-excitation system, load and power factor control, step-up and step-down transformers, and switchgear.The metering and instrument equipment is also described, particulars being given of both low- and high-frequency oscillographs and their associated components.

DOI:10.1049/jiee-1.1937.0090

出版商:IEE    

年代:1937

数据来源: IET

摘要:

The paper describes an experimental investigation, for simple conditions of short-distance propagation, of fading control of radio signals by methods which rely on transmission being made on adjacent frequencies. It has been found that the frequency separation of the signals required for optimum fading control is determined by the path-difference between the ground and sky rays and is independent of the mean frequency of the wave.In general it is necessary to read messages on such circuits by observing the change in direct current in the detector at the receiver, since the audio-frequency components are uncontrolled.Applications of the system of fading control are suggested in connection with ionospheric research, direction-finding, and broadcast telegraphy and telephony.The most satisfactory type of controlled transmission involves suppressed-carrier technique. The use of this system in short-distance propagation ensures that the night-time signal never falls below that due to the ground ray alone. In long-distance transmissions, to be described later, the effect of the control is to remove the deep troughs of fading.

DOI:10.1049/jiee-1.1937.0093

出版商:IEE    

年代:1937

数据来源: IET

摘要:

The paper describes a continuation of fading-control experiments by methods which rely on transmissions being made at adjacent frequencies. Measurements have been made at distances of 700 and 3 300 km. from the transmitter, and it is found that phase-fading is due to interference between two main sky-rays of comparable intensity. The path-differences between these rays have been measured with the help of the Appleton-Barnett frequency-change technique and the corresponding control modulations applied.The most satisfactory type of controlled signal is obtained by imposing two modulations having frequencies in a 3 : 1 ratio and by suppressing the carrier. The optimum control frequencies were found to be 200 and 600 cycles when the distance between sender and receiver was 700 km., whereas at 3 300 km. the best frequencies were 50 and 150 cycles.Reception of the doubly-modulated signals shows that, when the control frequencies have been adjusted to correspond to the sky-ray path-differences, the phase-fading is eliminated. This removes all of the deep troughs of fading, and the residual intensity variations are then well within the capabilities of simple automatic-volume-control apparatus at the receiver.

DOI:10.1049/jiee-1.1937.0094

出版商:IEE    

年代:1937

数据来源: IET

摘要:

Certain symmetrical light distributions described briefly by the author in a previous paper are here considered at greater length. They possess, among other properties, that of producing uniform illumination on the horizontal plane in large lighting systems. The effect of varying the spacing/height ratio in a given system is here dealt with. Alternative methods of testing lighting fittings are described. The conclusion is reached that these light distributions may in some cases be regarded as the best that could be employed in practice, and in others as approximately the best. It is pointed out, however, that uniformity of illumination is often only one of a number of requirements that have to be met, and practical light distributions may be modified by this consideration and by the desirability of obtaining a high luminous efficiency.

DOI:10.1049/jiee-1.1937.0096

出版商:IEE    

年代:1937

数据来源: IET

摘要:

The paper summarizes the development of high-permeability alloys from early researches to the commercial products of the present day.The difficulties encountered during manufacture, and the precautions necessary in these metallurgical processes, are described.Stress is laid on the correct methods of application to ensure that the magnetic properties of the alloys are utilized to full advantage, and the need for heat treatment is emphasized . Propositions are put forward to explain the mechanism of this heat-treatment process, and the practical procedure is given.Data on curves show the electrical and magnetic properties of the alloys.The paper finally discusses the practical applications of high-permeability materials, giving examples of commercial instruments and indicating cases in which their extended use would be advantageous.

DOI:10.1049/jiee-1.1937.0098

出版商:IEE    

年代:1937

数据来源: IET

DOI:10.1049/jiee-1.1937.0103

出版商:IEE    

年代:1937

数据来源: IET